What is the difference between the source of a river and the mouth of a river?

The source is the farthest point of the river stream from its estuary or its confluence with another river or stream. Rivers are usually fed by many tributaries. ... The source is where a river begins, and the river mouth is where it joins the sea. The mouth may be in the form of a river delta.

the answer should be a. the sui empire, the tang empire extended from korea in the west to manchuria in the east.